Yarn supplied to a yarn supply drum at a tangent via a supply guide element and drawn off from the drum, oriented outward, at a yarn take-off speed that corresponds to the yarn supply speed, via a run-off guide element disposed laterally beside the yarn drum. The run-off guide element is stationary and is disposed spaced apart from and below the lower rim of the yarn drum. Associated with the yarn drum are a supply yarn monitor, which, with a supply yarn sensor feels the supplied yarn prior to the supply guide element. A run-off yarn monitor, which, with a run-off sensor, feels the yarn as it is taken off in the vicinity of the run-off guide element.
A yarn supply apparatus of this kind is known, e.g., from German Patent DE-PS No. 26 08 590. The supply guide element here is formed by a yarn eye, which is stationary on the holder carrying the yarn drum and is located after the yarn brake in the path of yarn travel. The supply yarn sensor senses the supplied yarn on the yarn travel path between the yarn brake and this yarn eye. The yarn eye must be located a specific minimum distance from the circumference of the yarn drum, in order to prevent the yarn from being deflected to the side too abruptly on its way from the yarn eye to the circumference of the yarn drum. Because of this spacing of the yarn eye from the yarn drum, the yarn can change its direction of travel to the yarn drum if the tension on the supplied yarn changes, and this can have an undesirable influence on the buildup of the storage winding on the yarn drum.
In this known yarn supply apparatus, the storage winding formed on the yarn drum is compelled to advance axially on the yarn drum in a continuous manner by a feed device, in the form of a feed wheel driven by the yarn drum; in the event that yarn is not being drawn off, this prevents windings of the storage winding from shifting upward past the rim of the yarn drum.
In yarn supply apparatuses operating without this kind of compulsory feed device for the storage winding, and in which a specialized, in particular conical, shape of the yarn drum in the vicinity of where the yarn is wound on assures that the storage winding will be continuously advanced axially as it forms, the danger exists that if the yarn run-off is interrupted, the storage winding will be "overrun"; that is, the newly formed windings of the arriving yarn will shift upward past the upper rim of the yarn drum. Yarn drums of this kind are described in German Patent De-PS No. 27 43 749, German examined application DE-AS No. 17 60 738 and German Patent DE-PS No. 33 26 099, to name only a few examples.
The above danger that windings of the storage winding may emerge at the top beyond the rim of the yarn drum also exists whenever a knitting machine equipped with this type of yarn supply apparatuses is blown out with a jet of compressed air during operation, in order to clean out fluff. If the compressed air jet is handled carelessly, it may shift the arriving yarn out beyond the upper rim of the yarn drum because the yarn supply eye is so far from the yarn drum. The result is that the yarn becomes wound up above the yarn drum.
That eventuality, however, must absolutely be avoided.
Another important factor in proper functioning of yarn supply apparatuses of the above type is how the yarn runs off the yarn drum. If there is some disruption in the evenness of yarn run-off, for instance because torn-off filaments of the yarn are wound back onto the drum from below, or because loops or sags form in highly twisted yarn as it runs off, causing uneven yarn run-off or even causing the loops to be wound back on again, then this affects the removal of yarn from the storage winding and hence also affects the arrival of the yarn being supplied. Consequently the storage winding may no longer be capable of advancing properly, especially in the case of yarn drums where the axial advancement of the storage winding is effected over a conical surface where the yarn arrives, or the like, causing the newly formed windings to build up in the area of the surface where the yarn arrives and finally causing the yarn to be wound up above the yarn drum, as feared.